This British thriller, which plays on a yacht most of the time, deals with an accident concerning a sexual practice called Donkey Punch, whereby the man punches his female partner in the back of the neck shortly before he's getting an orgasm. This should drive her into unconsciousness while her muscles cramp and give the man a more intense sexual pleasure. But that's just a theory because the film shows this action going horribly wrong and a fight between the remaining passengers flaring up.

Considering the subject matter of the film it was obviously necessary to release two DVD editions of Donkey Punch in the US. On the one hand a censored version that got rated R by the MPAA, on the other hand an unrated version, being identical to the uncut BBFC 18-DVD released in the UK. But here's already the first thing that provokes questions because the R-rated DVD features a “Not Rated”-version as well! Except for two scenes where critical sexual content was zoomed in in order to avoid a full shot of the scenes, this is practically a variation of the uncut film. If that “unzooming” of the scenes is enough reason to release the unrated version as a stand-alone DVD lies in the eye of the beholder.
The only (and amateurish) censorship in the R-rated version can be found in short time camcorder recordings during the sex scene. Instead of working with alternate material the R-rated has a black cube being placed in front of the critical body parts of the actors. Even in the original version these shots are not really explicit because of the bad quality of the DV recordings but it seemed to be too much for the US market.
After all, the artwork and the choice of the screenshots on the cover of the unrated edition suggests the impression that there's a more gory cut of the film on the DVD. This is not the case, the violence is identical in both versions.

Comparison between the censored R-rated DVD and the Unrated DVD (equivalent to the original uncut UK-version) (both published by Magnolia Home Entertainment).

3 censored scenes with no time difference

R-Rated/Unrated: 0:31:29: Nothing's cut here. However, the R-rated version offers a black cube on Bluey's naked butt. The camera then changes to Kim having sex while her rear part is being “covered” the same way as Bluey's. Another camera panning back to Bluey and Lisa shows this censorship a third time.
No time difference

R-Rated:

Unrated:

R-Rated/Unrated: 0:33:12: As Lisa knees on the bed the camera pans down at her body showing her genital area. The R-rated version covers that with a black cube.
No time difference

R-Rated:

Unrated:

R-Rated/Unrated: 0:34:43: While Josh works on Lisa from behind and gets cheered at by Bluey, not much can be seen in detail. But it appears that this still was enough to be censored and zoomed-in in the R-rated version.
No time difference